Jet pump

ABSTRACT

A jet pump includes a housing having a first inlet for a first fluid, a second inlet for a second fluid and an outlet for a combined fluid comprising said first and second fluids. A nozzle assembly is removably received within the housing and configured to receive the first fluid from the first inlet, and a mixing tube/diffuser assembly removably received within the housing downstream of the nozzle assembly and configured to receive and combine the first and second fluids. The nozzle assembly and the mixing tube/diffuser assembly are removable from the housing through the first inlet.

CROSS REFERENCE TO RELATED APPLICATION

This application claims foreign priority under 35 USC 119 to British application no. GB 1504304.5 filed Mar. 13, 2015.

FIELD

The present invention relates to a jet pump and in particular, but not exclusively, to a jet pump for use in the oil and gas industries.

BACKGROUND

Jet pumps or eductors are passive devices that use energy from a high pressure (HP) fluid source to boost the pressure of a low pressure (LP) fluid. The terms jet pump, eductor, ejector and gas jet compressor are used in various industries and refer to the same general type of device. The HP and LP fluids may each consist of liquids, gases or a mixture of liquids and gases.

In the oil and gas production industry jet pumps have been used successfully in a variety of applications onshore or near the bottom of oil or gas wells. In such situations the HP fluid may be gas or a high pressure liquid such as oil or water. The LP fluid could be gas or liquid (oil and/or water), or a mixture of gas and liquid.

FIGS. 1 and 2 show the key features of a typical conventional jet pump system. HP fluid from a HP source passes through a HP delivery line 2 to a HP inlet 4 of a jet pump 6, where it passes through a nozzle assembly 8 that increases the velocity of the fluid. In this way part of the potential (pressure) energy of the HP fluid is converted to kinetic energy (high velocity fluid). As a result, the pressure of the fluid drops significantly in a nozzle discharge zone in front of the nozzle assembly 8.

LP fluid from a LP source passes through a LP delivery line 10 to a LP inlet 12 and is introduced into the jet pump 6 at the nozzle discharge zone in front of the nozzle assembly 8. The LP fluid is entrained in the flow of fluid emerging from the nozzle assembly 8. The combined fluids pass through a mixing tube/diffuser assembly 13 comprising an upstream mixing tube/diffuser 14 and a downstream diffuser 16. The fluids they are mixed together as they pass first through the mixing tube/diffuser 14, and momentum and energy are exchanged between the fluids. The combined fluids then pass through the expanding diffuser 16 where the flow velocity of the combined fluids decreases and pressure recovery takes place. The combined fluids then pass through an outlet 18 into an outlet line 20. The pressure of the combined fluids at the outlet 18 of the jet pump 6 will generally be at an intermediate value between the pressures of the HP and LP fluids at the inlets 4, 12.

For maximum efficiency, the dimensions of the nozzle assembly 8, the mixing tube/diffuser 14 and the diffuser 16 must be selected according to the pressures, flow rates and types of the HP and LP fluids delivered to the jet pump 6. In some jet pumps, for example as described in GB2384027B, the nozzle and the mixing tube/diffuser assembly comprise replaceable components that are mounted within a housing. This allows the components to be removed and exchanged if the operating conditions change.

In the jet pump system described in GB2384027B, the nozzle assembly is designed to be removed and replaced through the HP inlet end of the jet pump, while the mixing tube/diffuser assembly is removed and replaced through the outlet end of the jet pump. As a result the process of replacing the internal components when the jet pump is installed in a gas or oil production system is complicated. If replacement of the internal components is needed, spool pieces comprising flanged lengths of pipe (not shown) must be removed from both ends of the jet pump to provide access to the internal components. Sufficient space must be available at both ends of the jet pump to allow the nozzle assembly and the mixing tube/diffuser assembly to be pulled out of the housing. In some cases the mixing tube/diffuser assembly may have a length of a few metres, requiring the removal of a very substantial length of pipe. After the new internal components have been installed the spool pieces have to be reinstalled, followed by tightening of the bolts at both ends of the jet pump and checking the system for leaks. The operation is therefore costly and time consuming. The mixing tube/diffuser assembly can also be a very expensive component, particularly if it is of a large size.

The jet pump system described in GB2384027B requires that a gap is provided between the mixing tube/diffuser assembly and the housing, which is in fluid communication with the fluids passing through the jet pump. The internal pressure within the jet pump is therefore carried entirely by the housing. This feature is designed to ensure that the internal and external pressures acting on the mixing tube/diffuser assembly are equalised, so that it does not require great strength. However, if the passage of fluids into the gap were to become blocked this could lead to failure of the mixing tube/diffuser assembly.

SUMMARY

It is an object of the present invention to provide a jet pump that mitigates one or more of the aforesaid disadvantages.

According to one aspect of the present invention there is provided a jet pump including a housing having a first inlet for a first fluid, a second inlet for a second fluid and an outlet for a combined fluid comprising said first and second fluids, a nozzle assembly removably received within the housing and configured to receive the first fluid from the first inlet, and a mixing tube/diffuser assembly removably received within the housing downstream of the nozzle assembly and configured to receive and combine the first and second fluids, wherein the nozzle assembly and the mixing tube/diffuser assembly are removable from the housing through the first inlet.

The configuration of the jet pump makes it possible to remove both the nozzle assembly and the mixing tube/diffuser assembly through the first inlet of the housing, without disconnecting the outlet line from the jet pump. The internal components of the jet pump can therefore be removed and replaced relatively quickly and easily, thus enabling the jet pump to be adapted readily to different operating conditions for efficient operation.

The mixing tube/diffuser assembly may include an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion. In one embodiment the upstream mixing tube portion of the axial bore has a substantially constant cross-sectional area and the downstream diffuser portion has a cross-sectional area that increases towards the downstream end of the mixing tube/diffuser assembly. Optionally, the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly. The second diffuser portion may comprise a continuation of the first diffuser portion. In other words it may have a complementary profile. For example the second diffuser portion may have the same taper angle as the first diffuser portion and it may have a diameter at its upstream end that matches the diameter at the downstream end of the first diffuser portion.

By dividing the diffuser into two portions, comprising a first portion that forms part of the mixing tube/diffuser assembly and a second portion that forms part of the housing, the length of the mixing tube/diffuser assembly can be reduced. This reduces the cost of the mixing tube/diffuser assembly and makes handling easier, particularly when installing or replacing the mixing tube/diffuser assembly in the housing.

The possibility of dividing the diffuser into two portions is based on the realisation that only the upstream part of the diffuser has to be replaced in order to adapt the jet pump to different operating conditions. The downstream portion of the diffuser does not have to be changed and this portion can thus be formed in the housing, providing the advantages discussed above.

Optionally, the nozzle assembly and the housing include complementary stop members that are configured to limit movement of the nozzle assembly towards the outlet. Optionally, the mixing tube/diffuser assembly and the housing include complementary stop members that are configured to limit movement of the mixing tube/diffuser assembly towards the outlet. The provision of stop members ensures that the nozzle assembly and the mixing tube/diffuser assembly are correctly located within the housing.

According to another aspect of the invention there is provided a jet pump including a housing having a first inlet for a first fluid, a second inlet for a second fluid and an outlet for a combined fluid comprising said first and second fluids, a nozzle assembly removably received within the housing and configured to receive the first fluid from the first inlet, a mixing tube/diffuser assembly removably received within the housing downstream of the nozzle assembly and configured to combine the first and second fluids, wherein the mixing tube/diffuser assembly includes an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion, and wherein the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly.

As indicated above, by dividing the diffuser into two portions the length of the mixing tube/diffuser assembly can be reduced. This reduces the cost of the mixing tube/diffuser assembly and makes handling easier, particularly when installing or replacing the mixing tube/diffuser assembly in the housing

In an embodiment the mixing tube/diffuser assembly includes an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion. Optionally, the upstream mixing tube portion of the axial bore has a substantially constant cross-sectional area and the downstream diffuser portion has a cross-sectional area that increases towards the downstream end of the mixing tube/diffuser assembly. The second diffuser portion optionally comprises a continuation of the first diffuser portion.

In an embodiment the first fluid has a higher pressure than the second fluid. For example, the first fluid may be a high pressure (HP) fluid and the second fluid may be a low pressure (LP) fluid.

Optionally, the housing includes an elongate tubular body, the first inlet is located at an upstream end of the tubular body and the outlet is located at a downstream end of the tubular body. Optionally, the first inlet and/or the outlet are aligned with the longitudinal axis of the tubular body. Optionally, the first inlet is the HP inlet for HP fluids.

Optionally, the second inlet extends through a circumferential wall of the tubular body and opens into the tubular body downstream of the nozzle assembly and upstream of the mixing tube/diffuser assembly.

Optionally, the nozzle assembly is configured to discharge the first fluid into a discharge zone downstream of the nozzle assembly and upstream of the mixing tube/diffuser assembly.

Optionally, the mixing tube/diffuser assembly is sealingly received within the housing to prevent fluid communication into a region between the mixing tube/diffuser assembly and the housing. This avoids the risks associated with the requirement to provide a fluid passageway into a gap between the mixing tube/diffuser assembly and the housing, as outlined above.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side view of a known jet pump system;

FIG. 2 is a sectional isometric view of a known jet pump, and

FIG. 3 is a sectional side view of a jet pump according to one possible embodiment of the invention.

DETAILED DESCRIPTION

The known jet pump and the jet pump system shown in FIGS. 1 and 2 are described above. A similar jet pump system is also described in GB2384027B. The jet pump of the present invention may form part of a jet pump system that includes one or more features of the known jet pump and jet pump system shown in FIGS. 1 and 2 including, but not limited to, the HP and LP inlet lines 2, 10 and the outlet line 20.

FIG. 3 shows a jet pump 26 according to a first embodiment of the invention, which is supported on stands 28. The jet pump 26 comprises a substantially cylindrical tubular elongate housing 30 having an upstream portion 32, a central portion 33 and a downstream portion 34. A first flange plate 36 is provided at the upstream end of the housing 30 and a second flange plate 38 is provided at the downstream end of the housing 30. The housing 30 also includes a side inlet pipe 40, which extends outwards from the housing substantially perpendicular to the longitudinal axis of the housing 30. The side inlet pipe 40 is provided at its outer end with an inlet flange plate 42 and comprises an inlet vent that extends through the circumferential wall of the housing 30 within the upstream portion 32 thereof.

The upstream portion 32 of the housing 30 provides an axial HP inlet 44, which may be connected to a HP delivery line 2 to receive a supply of HP fluid. The side inlet pipe 40 comprises a non-axial LP inlet 46 and may be connected to a LP delivery line 10 to receive a supply of LP fluid. The downstream second portion 34 of the housing provides an axial outlet 48 for fluids flowing out of the jet pump and may be connected to an outlet line 20.

A nozzle assembly 50 and a mixing tube/diffuser assembly 52 are removably mounted within the housing 30. The nozzle assembly 50 is located within the upstream portion 32 of the housing and includes a tubular cylindrical body 54 having a cylindrical mounting portion 56 at one end and a hollow conical nozzle portion 58 at the other end, which leads to a nozzle outlet 60. The mounting portion 56 includes a flange 62 that abuts the upstream end of the housing 30. The mounting portion 56 may also carry one or more O-rings (not shown) in grooves on its outer surface, to form a seal with the inner surface of the cylindrical housing 30. The nozzle assembly 50 may be withdrawn axially from the housing through the HP inlet 44 at the upstream end of the housing 30.

The mixing tube/diffuser assembly 52 comprises a tubular body that has a sliding fit within the central portion 33 of the housing 30. The tubular body of the mixing tube/diffuser assembly 52 has a longitudinal bore that includes a converging upstream portion 64, a central mixing portion 66 of substantially constant diameter and cross-sectional area, and a diverging first diffuser portion 68 at the downstream end of the mixing tube/diffuser assembly 52. The upstream portion 64, which comprises the inlet to the mixing tube/diffuser assembly 52, is located in the vicinity of the nozzle discharge zone 70, just downstream of the nozzle 60, to receive fluids discharged through the nozzle 60. The downstream end of the mixing tube/diffuser assembly 52 is located at the junction between the central and downstream portions 33, 34 of the housing.

The mixing tube/diffuser assembly 52 has a flange 71 at its upstream end, which engages a shoulder 72 at the upstream end of the central portion 33, and carries at each end an O-ring 73 that is located in a groove on the outer surface of the mixing tube/diffuser assembly 52. The O-rings 73 form a seal with the inner surface of the cylindrical housing 30. Any gap between the outer surface of the mixing tube/diffuser assembly 52 and the inner surface of the housing 30 in the central portion 33 is therefore isolated from the fluids flowing through the jet pump (i.e. the gap between the mixing tube/diffuser assembly 52 and the inner surface of the housing 30 is not in fluid communication with those fluids). Optionally, the gap may be filled with grease to prevent fluids from entering the gap.

The mixing tube/diffuser assembly 52 can be withdrawn axially from the housing 30 through the HP inlet 44 at the upstream end of the housing 30 (after the nozzle assembly 50 has been removed), thus allowing the mixing tube/diffuser assembly 52 to be removed and replaced. Optionally an extractor tool (not shown) may be provided, which can be used to engage the mixing tube/diffuser assembly 52, allowing it to be extracted from the housing. Alternatively, the mixing tube/diffuser assembly 52 may be connected to the nozzle assembly 50, so that the nozzle assembly 50 and the mixing tube/diffuser assembly 52 can be removed as a unit.

The downstream portion 34 of the housing 30 includes a tapered bore 74 that increases in diameter towards the downstream end of the housing 30. This tapered bore 74 comprises a second diffuser portion which provides a continuation of the first diffuser portion 68 at the downstream end of the mixing tube/diffuser assembly 52. Therefore, in this embodiment, the diffuser part of the jet pump comprises a combination of the first diffuser portion 68 at the downstream end of the mixing tube/diffuser assembly 52 and the second diffuser portion comprising the tapered bore 74 provided within the downstream portion 33 of the housing 30.

In use, a HP first fluid flows into the HP first inlet 44 upstream of the nozzle assembly 50 and is discharged through the nozzle opening 60 into the low pressure discharge zone 70 immediately downstream of the nozzle 60. The nozzle 60 increases the velocity of the fluid as it is discharged from the nozzle. In this way the potential (pressure) energy of the first fluid is converted to kinetic energy as the fluid emerges from the nozzle 60. This reduces the pressure within the low pressure nozzle discharge zone 70.

A LP second fluid flows into the LP second inlet 46 and is introduced into the low pressure nozzle discharge zone 70 downstream of the nozzle 60. The second fluid is combined in the nozzle discharge zone 70 with the first fluid emerging from the nozzle 60 and the combined first and second fluids are then mixed together as they flow through the mixing tube 66. The combined fluids then pass through the expanding diffuser 68, 74 where the velocity of the combined fluid normalises and pressure recovery takes place. Finally, the combined fluids exit the jet pump 26 at outlet 48. The combined fluids at the outlet 48 will generally be at an intermediate pressure value that lies between the pressures of the first and second fluids at the HP and LP inlets 44, 46.

In the present invention the nozzle assembly 50 and the mixing tube/diffuser assembly 52 can both be removed and replaced through the HP first inlet 44. Usually, a spool piece (a short length of pipe) attached to the HP first inlet 44 will be removed to provide access to the internal components of the jet pump. The nozzle assembly 50 and the mixing tube/diffuser assembly 52 can then be removed and replaced as required. It is not necessary to obtain access to the outlet 48 of the jet pump 26, thus avoiding any need to disconnect the jet pump outlet 48 from the outlet line 20. Further, because the mixing tube/diffuser assembly 52 includes only an upstream part 68 of the complete diffuser 68, 74 it has a reduced length as compared to the mixing tube/diffuser assembly of the prior art jet pump described above, which makes handling and replacement of the mixing tube/diffuser assembly easier.

Various modifications of the apparatus described above are of course possible. For example, instead of dividing the diffuser so that a first portion is part of the mixing tube/diffuser assembly and a second portion is part of the housing, the diffuser could be formed entirely within the mixing tube/diffuser assembly or entirely within the housing. In another embodiment, instead of removing the nozzle assembly and the mixing tube/diffuser assembly through an axial first inlet, the first and second inlets could instead be configured as non-axial inlets and the upstream and of the housing could be closed by a removable closure plate, which could be removed as required to provide access to the internal components of the jet pump, allowing the nozzle assembly and the mixing tube/diffuser assembly to be removed and replaced through the upstream end of the housing. 

1. A jet pump comprising: a housing including a first inlet for a first fluid, a second inlet for a second fluid, and an outlet for a combined fluid comprising said first and second fluids, a nozzle assembly removably received within the housing and configured to receive the first fluid from the first inlet, and a mixing tube/diffuser assembly removably received within the housing downstream of the nozzle assembly and configured to receive and combine the first and second fluids, wherein the nozzle assembly and the mixing tube/diffuser assembly are removable from the housing through the first inlet.
 2. A jet pump according to claim 1, wherein the mixing tube/diffuser assembly includes an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion.
 3. A jet pump according to claim 2, wherein the upstream mixing tube portion of the axial bore has a substantially constant cross-sectional area and the downstream diffuser portion has a cross-sectional area that increases towards the downstream end of the mixing tube/diffuser assembly.
 4. A jet pump according to claim 1, wherein the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly.
 5. A jet pump according to claim 4, wherein the second diffuser portion comprises a continuation of the first diffuser portion.
 6. A jet pump according to claim 1, wherein the nozzle assembly and the housing include complementary stop members that are configured to limit movement of the nozzle assembly towards the outlet.
 7. A jet pump according to claim 1, wherein the mixing tube/diffuser assembly and the housing include complementary stop members that are configured to limit movement of the mixing tube/diffuser assembly towards the outlet.
 8. A jet pump comprising: a housing including a first inlet for a first fluid, a second inlet for a second fluid, and an outlet for a combined fluid comprising said first and second fluids, a nozzle assembly removably received within the housing and configured to receive the first fluid from the first inlet, a mixing tube/diffuser assembly removably received within the housing downstream of the nozzle assembly and configured to combine the first and second fluids, wherein the mixing tube/diffuser assembly includes an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion, and wherein the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly.
 9. A jet pump according to claim 8, wherein the mixing tube/diffuser assembly includes an axial bore having an upstream portion comprising a mixing tube and a downstream portion comprising a diffuser portion.
 10. A jet pump according to claim 9, wherein the upstream mixing tube portion of the axial bore has a substantially constant cross-sectional area and the downstream diffuser portion has a cross-sectional area that increases towards the downstream end of the mixing tube/diffuser assembly.
 11. A jet pump according to claim 10, wherein the second diffuser portion comprises a continuation of the first diffuser portion.
 12. A jet pump according to claim 8, wherein the first fluid has a higher pressure than the second fluid.
 13. A jet pump according to claim 8, wherein the housing includes an elongate tubular body, the first inlet is located at an upstream end of the tubular body and the outlet is located at a downstream end of the tubular body.
 14. A jet pump according to claim 13, wherein the second inlet extends through a circumferential wall of the tubular body and opens into the tubular body downstream of the nozzle assembly and upstream of the mixing tube/diffuser assembly.
 15. A jet pump according to claim 8, wherein the nozzle assembly is configured to discharge the first fluid into a discharge zone downstream of the nozzle assembly and upstream of the mixing tube/diffuser assembly.
 16. A jet pump according to claim 8, wherein the mixing tube/diffuser assembly is sealingly received within the housing to prevent fluid communication into a region between the mixing tube/diffuser assembly and the housing.
 17. A jet pump according to claim 2, wherein the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly.
 18. A jet pump according to claim 3, wherein the housing includes a second diffuser portion that is located downstream of the mixing tube/diffuser assembly.
 19. A jet pump according to claim 5, wherein the nozzle assembly and the housing include complementary stop members that are configured to limit movement of the nozzle assembly towards the outlet.
 20. A jet pump according to claim 5, wherein the mixing tube/diffuser assembly and the housing include complementary stop members that are configured to limit movement of the mixing tube/diffuser assembly towards the outlet. 